1. Field of the Invention
The present invention is related to a chemical copper-plating bath.
2. Description of the Related Arts
Chemical copper-plating baths, also referred to as electroless copper-plating baths, consist of a copper salt, a complexing agent, a reducing agent, and a pH-adjusting agent. Such a chemical copper-plating bath has a disadvantage of a slow plating deposition speed ranging from 1 to 2 .mu.m/hr, which is partly attributable to a great reduction in the depositing speed caused by the presence of additives (such as potassium ferrocyanide, 2,2'-bipyridyl, and the like) for improving the physical properties of a copper plating film. Namely, the plating deposition speed in the bath consisting of a copper salt, a complexing agent, a reducing agent, and a pH-adjusting agent is as high as 10 .mu.m/hr, but if additives are present in the bath, the plating deposition speed is reduced to 1.about.2 .mu.m/hr. Accordingly, if a high speed, thick plating deposition is required, copper-plating films are usually formed by an electrolytic deposition of copper. For example, a method for forming conductors on a printed circuit by chemical copper plating (referred to as the additive method) is used, and has advantages such as the attachment of electrodes to the workpiece becomes unnecessary for the formation of a conductor circuit, and thus costs are reduced and the process is simplified. The additive method also makes it possible to enhance the integration of conductor circuits, and thus the realization of fine conductor lines. Nevertheless, this additive method can be practiced only by providing a chemical copper plating bath by which a high speed and thick deposition of copper plating can be achieved, and much research has been carried out into the discovery of such a chemical copper plating bath. According to research into chemical copper plating bath compositions which have been carried out in an attempt to meet the requests for a high speed and thick plating deposition, it has been proposed to add a trace amount of a stabilizing agent and an activating element to the bath with the above described general composition. The plating deposition speed attained by such a proposal is generally as high as 10 .mu.m/hr.
According to Japanese Unexamined Patent Publication No. 59-25965, a plating deposition speed of approximately 72 .mu.m/hr (at 70.degree. C.) is attained by using as the accelerating agent 2-mercaptobenzothiazole, imidazole, 4-hydroxypyridine, pirindine, or a compound of thereof. However, this accelerating agent must be used in only a small amount, and thus control of the bath is difficult.